(See article The Ear to get familiar with some terms in this article.)
Noise-Induced Hearing Loss a. k. a. NIHL is a hearing disorder caused by the exposure to intense sounds that can be divided into:
a short exposure to an extremely loud sound (an explosion, a gun shot, airplane,...) – acoustic trauma,
a long exposure to loud sounds (loud music, noisy workshop, construction site, …) – gradually developed.
NIHL causes a hair cells damage. These are a very sensitive part of the inner ear and when damaged, they don't grow back again.
Whatever happens in the sound intensity range under 75 dB is relatively safe (see article Sound to get familiar with this scale).
Whatever goes beyond that needs extra caution. Keep in mind that the louder the sound, the shorter the time period before NIHL can occur.
The areas that are severely exposed to this type of hazard are: agriculture, mining, construction, manufacturing, transportation, military, music (musicians, sound engineers, …).
Listening to music
Even if we are professionally not involved in any of the areas above, we daily listen to artificial sound sources (music, TV). Surely, music needs to be listened to at a proper volume to reveal its true dynamics, but it is also important not to exceed safe parameters. Listening to music through headphones needs particular attention,because the sound pressure is concentrated directly into the ear. Resting ears between listening sessions can be very beneficial to the ears, so they can recover.
The damage caused by the elevated sound volume can be temporary or permanent. In the case of a temporary hearing loss, the ear takes 16–48 hours to recover.
A permanent hearing damage can be of various intensities, from loosing the perception of a higher frequency range (muffled sound) to a partial or complete hearing loss (deafness).
Several studies have been conducted in the NIHL area. Some nutrient based options exist, like antioxidants or elevated doses of magnesium. Both need to be taken shortly after the exposure (a few days maximum). There are some genetic based options that may help regrow the damaged hair cells. Nothing of the above mentioned has been really proven to work well, so the best way to avoid NIHL is just to avoid it with a proper protection.